Plasmoids and sheaths mean success or failure for solar eruptions

April 19, 2011, Royal Astronomical Society
A simulation of the evolution of plasma density in an experiment where the eruption of the plasmoid is 'failed'. The dense material rises but it does not manage to break through the sheath magnetic field. Credit: Vasilis Archontis

Our Sun experiences regular eruptions of material into space, but solar physicists still have difficulty in explaining why these dramatic events take place. Now a group of scientists from the University of St Andrews think they have the answer: clouds of ionized gas (plasma) constrained by magnetic fields and known as 'plasmoids' that struggle to break free of the Sun's magnetic field. Dr Vasilis Archontis will present their work on Monday 18 April at the National Astronomy Meeting in Llandudno, Wales.

Active regions on the solar surface are often the site of eruptions. These are associated with magnetic fields from the solar interior rising to the surface and gradually expanding into the Sun's , the corona, in a process known as emergence.

The St Andrews team developed 3D computer models of these phenomena, revealing that the emergence of magnetic flux naturally leads to the formation and expulsion of plasmoids that adopt a twisted tube configuration.

The formation of the plasmoids is due to the motion of plasma in the lower atmosphere of the Sun. These motions bring magnetic fieldlines closer together to reconnect and build a new magnetic flux system (i.e. the plasmoid). Whether the plasmoids are 'failed' or 'successful' (i.e. they erupt into space) depends on the level of interaction between the new emerging field and the old, pre-existing in the .

A simulation of the evolution of plasma density in an experiment where the eruption of the plasmoid is 'successful'. The dense material rises slowly first, but eventually it accelerates to experience a rapid ejection out through the solar corona (at the top). Credit: Vasilis Archontis

When the new emerging field expands into the corona, it forms a 'magnetic sheath' with a fan-like shape. The sheath magnetic field consists of loop-like fieldlines, which are anchored to the and enclose the plasmoids.
A striking result from the simulations is that the plasmoids remain trapped in the if the magnetic sheath is not removed by some other external mechanism. In this case, the sheath fieldlines manage to stop the plasmoids erupting.

But if the sheath magnetic field breaks and connects with the other magnetic fields in the surrounding solar corona, the researchers believe that this opens the way for the plasmoids to erupt at speeds of up to at least 500 km per second. During the faster part of this eruption the plasmoids are pushed up, transfer heavy plasma to the solar corona, expand without constraint and accelerate out into space.

Explore further: Skeleton Of Sun's Atmosphere Reveals Its True Nature

Related Stories

Skeleton Of Sun's Atmosphere Reveals Its True Nature

April 16, 2007

The Sun's outer atmosphere or corona is incredibly complex, as shown in observations from space. It is also extremely hot, with a temperature of over a million degrees by comparison with that of the Sun's surface of only ...

Science with the solar space observatory Hinode

March 20, 2008

The solar space observatory Hinode was launched in September 2006, with the name "Hinode" meaning sunrise in Japanese. The Hinode satellite carries a solar optical telescope (SOT), an X-ray telescope (XRT), and an EUV imaging ...

How space eruptions happen

April 7, 2009

( -- Mathematicians at the University of St Andrews have made a discovery which could lead to a better understanding of why huge eruptions occur in space.

Giant pipe organ in the solar atmosphere

April 19, 2007

Astronomers have found that the atmosphere of the Sun plays a kind of heavenly music. The magnetic field in the outer regions (the corona) of our nearest star forms loops that carry waves and behave rather like a musical ...

The Sun's X-file under the Spotlight

September 3, 2004

One of the Sun's greatest mysteries is about to be unravelled by UK solar astrophysicists hosting a major international workshop at the University of St Andrews from September 6-9th 2004. For years scientists have been baffled ...

Recommended for you


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (2) Apr 19, 2011
Thanks for an interesting report.

Understanding solar eruptions is a formidable task, that may be impossible if the solar model is wrong.

See: "Superfluidity in the solar interior: Implications for solar eruptions and climate," Journal of Fusion Energy 21 (2002) 193-198
1 / 5 (1) May 12, 2011
But if the sheath magnetic field breaks and connects with the other magnetic fields in the surrounding solar corona

Magnetic fields do not break. The fallacy that says they do (and belief in this fallacy) is leading many fields of research down the path to utter nonsense, and will leave many good researchers either existing in a perpetual delusion, or with damaged careers.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.